It is generally well recognized in the polyurethane art that polyester polyurethanes tend to undergo thermal degradation during storage.
Attempts have been made to stabilize said polyurethanes, see U.S. Pat. No. 3,193,522, Neumann et al., which discloses the use of polycarbodiimides having a plurality of carbodiimide groups for said purpose. Also, Canadian Pat. No. 891,552 and Belgian Pat. No. 816,688 disclose methods of stabilizing polyester based polyurethanes using epoxides.
Although the carbodiimides afford a degree of stability to the polyester polyurethanes, they are added to stabilize the urethanes against hydrolytic degradation and have not been shown to be effective against thermal degradation. The Canadian and Belgian patents both teach the incorporation of epoxides into polyester based polyurethanes to stabilize them against hydrolytic degradation only. The Canadian patent however, does not disclose the small amounts of epoxide additive used herein or that amounts of epoxide over 1.0% do not impart thermal stability to the urethane.
The Belgian patent, although disclosing low amounts of epoxide additives, does not recognize the criticality of amounts below about 1.0% regarding thermal stability.
Accordingly, it is a primary object of the present invention to provide thermally and storage stable polyesterurethane compositions.
It is another object of the invention to provide a method for the preparation of thermal and storage stable polyesterurethane compositions.